1. Field of the Invention
The present invention relates to a molded and shaped insulating vehicle panel, particularly to such a panel that is acoustically insulating, and to a method for making that panel. More particularly, the present invention is directed to such panels that are used in assembling automobile and truck vehicles, such as door panels, roof panels, backlight panels and wheel wells, and especially the latter.
2. Description of Background Art
There has been a continued effort in the art to reduce the cost and weight of motor vehicles. A large part of the cost and weight is that of the metal parts used in the construction, e.g., body parts, protective and acoustical panels, and the like. While the present invention is widely applicable to vehicle panels, the present invention can be best illustrated by specific reference to automobile and truck wheel well shields. These shields are positioned underneath the wheel well of the vehicle and block splashed water and road debris from entering the vehicle underbody or engine compartment. Wheel well shields are a particularly difficult problem in the art, since these shields must not only prevent substantial egress of splashed water from the road into the underbody or engine compartment, but in order to be fully satisfactory must abate road noises occasioned by debris being spun by the tires into the wheel well. Of notable example of such noise is when an automobile traverses a gravel road, gravel is spun into the wheel wells by the tires and makes a very objectionable noise when the wells are unprotected or protected by shields that do not sufficiently acoustically abate that noise.
Traditional solutions for providing protection around the wheel well of a vehicle utilize stamped steel, and the like. These types of solutions were very effective in providing physical protection to the engine compartment and body structures, but were not effective in reducing vehicle noise levels. Additionally, due to the high stiffness and low damping properties, these shields generate unwanted noise in many situations where debris or water impact the shield and excite the structure so as to cause vibrations. These unwanted noises often result in ringing or panging sounds as water splashes or road debris impacts the shield.
There have been improvements on these traditional systems by applying damping coatings to the wheel well or shield or by using materials with lower mechanical stiffness. One such material that is commonly used today is polypropylene. This material can be molded into complex three dimensional shapes through compression or injection molding. The molded polypropylene shields provide weight savings over stamped metal and offer some improvement in acoustics through lower stiffness and higher internal damping properties. However, they do not meet current demands for noise abatement.
In this latter regard, an early effort for such noise abatement is disclosed in U.S. Pat. No. 1,704,048, which proposes applying a thin rubber shape to underneath a fender, which shape is impervious to water, and by way of its elasticity deadens road noise such as gravel. On the other hand, U.S. Pat. No. 3,068,794 proposes fender boots, which are placed inside of the wheel well. The fender boots are made of a plastic material to abate road noises.
In a more recent approach, U.S. Pat. No. 4,620,745 describes wheel well protectors having semi-resilient material for noise abatement. U.S. Pat. No. 4,735,427 goes even further toward modern applications in that it proposes a shell of plastic material contoured approximately to the contour of the wheel well. Preferably, the plastic material is a needled plastic fiber fleece material that is produced from sheet material by warm working to the contours of the wheel well, and is secured to the wheel well by adhesion, gripping screws, and the like. An alternative in this protective device is where, for special sound insulation, the fleece material can be made impermeable to water on its front side by use of elastic plastic material. This is, essentially, the approach most currently used in the background art.
However, as a more advanced approach, U.S. Patent Application Publication No. 2004/0096646A1 proposes a light weight wheel shield made of plastic for the reduction of rolling noises, sprayed water noises, and stone impact noises by use of foamed or expanded plastic. That publication also references various attempts at wheel well shields and points out that the expanded plastic wheel well shield of the invention is surprisingly stable in shape and has excellent acoustical properties, as well as being light weight. The wheel well shield can be produced by injection molding or deep drawing. This more modern approach in the background art is significant in that it recognizes the need to make the wheel well shield as light weight as possible, while providing good sound abatement.
It is therefore quite clear that successful wheel well shields depend on the particulars of the material from which the shield is made, especially in regard to noise abatement. In this latter regard, U.S. Pat. No. 5,094,318 proposes a sound absorption material for automobiles, which is a combination of layers with a dampening sheet therein. U.S. Pat. No. 4,801,169, which is particularly directed to a trunk liner, makes clear the importance of the vehicle panel being self-supporting, since the self-supporting nature can facilitate application and fastening of the panel to the vehicle. In particular, that patent suggests a molded trunk liner formed of fibrous material, such as polyester staple fibers that have been needle punched with a moldable coating applied to a backside of the liner to provide shape retention and stiffness. Coatings of polyethylene or moldable latex are suggested. U.S. Pat. No. 4,673,207 discloses a similar trunk liner where the panels are biased inwardly toward an upright position when mounted in the trunk to facilitate mounting. U.S. Pat. No. 4,568,581 is similar but proposes the use of molded panels for trunk compartments comprising a non-woven web formed of a blend of relatively high melting fibers and relatively low melting thermoplastic fibers where the low melting fibers form a multiplicity of bonds imparting shape retention and on one surface a fused form.
Recently, a substantial advance in the art in acoustical insulation has been proposed in U.S. Patent Application Publication No. 2003/0199216A1, assigned to the present Assignees. That application points out that acoustical insulation, especially for vehicle panels, generally has low x-y plane strength unless they are of substantial thicknesses or composed of multi-layers, one of which is a strength producing layer. However, most applications for automobile acoustical insulation must be contained in relatively small spaces, and generally must be one inch or less in thickness. This is true for automobile panels, and is also true for wheel well shields. That application proposes a gradient density material made of a single layer of non-woven material which has been processed such that at least a portion of the thickness has a density increase with respect to the remaining portions of the thickness, and the single layer material, after processing, has an air flow resistance in the range of 200 to 4000 MKS rayls, which, as disclosed in that application, is the range necessary for good acoustical abatement. This is a substantial advantage in the art, and the publication is incorporated herein by reference.
Thus, it is clear that the art has long sought to provide better vehicle panels that have substantial acoustical abatement and, especially, such panels that are also self-supporting. The present invention is directed to providing specific panels of that nature but which can be produced at a relatively low cost and with high acoustical abatement.